Cathode-ray tube



March 27, 1945. STAMER 2,372,455

CATHODE-RAY TUBE Filed June 2, 1943 m INVENTOR.

JAM;

Patented Mar. 27, 1945 CATHODE-RAY TUBE Andrew F. Stanler, Passaic, N. J assignor to Allen B. Du Mont Laboratories, Inc., Passaic, N. 1., a corporation of Delaware Application June 2, 1943, Serial No. 489,367

3 Claims.

This invention relates to electronic tubes such as audions or cathode-ray tubes, for example, although it is not restricted to such vacuum tubes. The invention relates more particularly to the cathodes of these tubes.

Heretofore cathodes for electronic tubes have been made of metal or compositions which will,

upon being heated, emit electrons. In order to increase the emissivity of electrons, different sorts of compositions and alloys have been used in making the cathodes, and the surfaces from which electrons were to be emitted were coated with materials such as oxides of metals, or other oxides such as calcium, barium or caesium oxide, for example, to increase the emissivity.

It has been found, however, that very small amounts of impurities in the cathodes escape from the metal at the high temperatures needed for satisfactory electron emission, and that these impurities poison the electron-emitting material and greatly decrease its emissive power.

By the present invention this diiflculty is overcome, and the danger of the electron-emissive material becoming poisoned or weakened in its ability to emit electrons at elevated temperatures is avoided.

In the drawing, a vacuum tube such as is used for producing a cathode-ray beam is shown somewhat diagrammatically for illustrative purposes.

Fig. 1 is a side view of a cathode-ray tube; and Fig. 2 is a side view of the cathode of this tube on an enlarged scale.

In the drawing, reference characterl indicates the evacuated tube that is provided with a heater 2, cathode 3, control grid 4, first anode 5, second anode 8, and pairs 1 and 8 of deflection plates for the cathode-ray beam. .7

The face of the cathode 8 is coated with material III that has the characteristic of emitting a very large number 01' electrons when heated.

The gist of this invention is to prevent this emissive material ill from becoming contaminated with impurities-that would decrease the emis- 35 a substantially pure carbon sivity. It has been found that the metals or materials which have been used heretofore for making cathodes contain enough impurities, even when refined by the best known methods, to contaminate the layer of emissive material sufflciently'to reduce the emissivity very greatly.

In accordance with the present invention it has been found that graphitic carbon can be commercially obtained in such a purified state that it can 10 be satisfactorily used for making the cathode 3,

and that when so used the electron-emissive material H), such as oxides of metals or oxides of cadmium, barium and caesium, for example, mentioned above, can be applied as indicated in Fig.

2. The purified carbon or graphite used in making the cathode 3 will withstand sufiicient heat to heat the coating ID to the desired temperature for emitting electrons at the desired rate, and no noticeable contamination of this material Ill occurs during the normal life of the tube I.

Poisoning of the electron-emitting material is avoided by this invention. Graphite can be obtained in a very pure state, and the occluded gas can be completelyremoved therefrom, thereby obviating possible trouble from that source. And

.since secondary electron emission from metal is avoided, better spot characteristics can be ob tained in cathode-ray tubes with this invention. What is claimed is:

1. A cathode for a cathoderay tube, consist- I ing or a substantially pure carbon support having a depression therein and emissive material locat-- ed in said depression. v

2. A cathode-ray tube electrode constructed of tupport having a surface depression therein in which cathode-emissive material which has a high coemcient of electron 4 emissivity is located.

8. The cathode of claim 1, in which the carbon 40 is graphite irom which occluded gas has been 

